BTG1 is a transcription regulatory protein that interacts with different transcription factors and nuclear receptors. BTG1 acts as a tumor suppressor and as a mediator of myogenic and erythroid differentiation. BTG1 transcription is positively regulated by FOXO3a, a member of FOXO family of transcription factors that have been associated with longevity and tumor suppression. Compounds that stimulate BTG1 transcription may have potential applications in aging, cancer and musculoskeletal diseases. Some BTG1-inducing compounds, however, also have an undesirable effect, as they induce cyclin-dependent kinase inhibitor p21 (CDKN1A), which in its turn activates a group of genes implicated in cancer and age-related diseases. Cell-based screening assays for compounds that activate either BTG1 promoter or a p21-responsive promoter have been developed for identifying inducers of BTG1 transcription that do not activate p21-inducible transcription. The goal of the proposed Phase 1 STTR program is to identify compounds that induce BTG1 transcription without significant toxicity to normal cells and without inducing p21-responsive disease-associated genes. The specific aims of this proposal are as follows. (1) Using a collection of ~1,000 diverse compounds with growth-inhibitory activity, selected in a preliminary screen from >100,000 drug-like small molecules and known drugs, screen for compounds that stimulate BTG1 promoter activity. (2) Test BTG1 inducers identified in Aim 1 for their ability to induce BTG1 promoter in different cell lines and to activate transcription from a p21-responsive promoter. Identify compounds that induce BTG1 promoter in different cell types with little or no concurrent induction of p21-responsive transcription. (3) Test BTG1 inducers identified in Aim 2 for their ability to induce cell growth arrest and cell death in different types of normal and tumor cells, as well as in p53 wild-type and p53-null cells. Identify BTG1 inducers that show tumor-selective growth inhibition, or induce little or no cytoxicity in normal cells. (4). Test BTG1 inducers selected in Aim 3 for their effects on FOXO3a-dependent transcription, FOXO3a protein expression, nuclear translocation and phosphorylation by Akt. Identify BTG1 inducers that activate FOXO3a as potential candidates for target-based lead optimization. In studies envisioned under the future Phase 2, BTG1-inducing agents that do not activate p21-responsive transcription will be investigated for their spectrum of activity in aging, cancer and muscular dystrophy. In addition, structure-activity relationship analysis will be carried out for the most selective and efficacious compounds, and the results of this analysis will be used to drive the process of chemical optimization of BTG1 inducers as potential drug leads. [unreadable] [unreadable] [unreadable]